Assemblies of fuel cells, called cell stack assemblies (CSA), have been used for some time as power sources for stationary fuel cell power plants in units such as ONSI's PC25 power plant; and they have also been used as power sources in space for NASA's Space Shuttle orbiter vehicle which is powered by International Fuel Cells Corporation's PC17 power plant. In view of their size, weight and/or cost, neither of these units is adaptable for use in a mobile vehicle application; however experimental units are being developed for use in mobile vehicles that will meet the size, weight and cost requirements and will also run on a reformable fuel, such as gasoline, diesel fuel, or the like.
A primary operating parameter that must be addressed in the use of a fuel cell power plant in a mobile vehicle is the start-up sequence. For example, the aforesaid PC25 power plant requires about three hours to achieve startup conditions; while the orbiter PC17 unit requires less than an hour to achieve startup conditions. Neither of these startup time requirements is acceptable for a mobile vehicle application. A fuel cell powered mobile vehicle must be able to be started as easily as an internal combustion engine-powered vehicle, which is ready to operate as soon as the ignition is turned on. Thus, the development of a system with instant ignition response at vehicle start-up is a necessary objective for a fuel cell power plant system that is able to be used to power a conventional mobile vehicle, such as an automobile, bus, truck, or an aquatic vehicle such as a boat.
The fuel cell CSA of a fuel cell power plant, especially a PEM type fuel cell which operates at relatively low temperatures, can be designed to deliver startup power evenly before achieving full CSA operating temperatures. Yet, to have a fuel cell powered vehicle system that runs on reformate gas operate instantly at start-up, one needs a system operating method for the initial transient time required to start the fuel processing unit. The key elements of the fuel processing unit, i.e., the sulfur scrubber and reformer, take a finite amount of time to be raised to their predetermined operating temperatures, while at the same time, the vehicle is required to operate according to the driver's demands without delay. One approach followed by some experimental developers is to eliminate the fuel processing problem by defining the power plant solely as a pure hydrogen fuel unit. Since gasoline is the most generally available fuel for vehicular use, a fuel cell power plant that can use gasoline, or similar commonly available vehicle fuels would be most desirable.
Since gasoline or similar fuels are preferred for vehicular applications, it is necessary to employ a fuel processing technique that can readily convert these fuels into a hydrogen-rich fuel stream while also lending itself to a light weight and compact design. An autothermal fuel processing unit, as described in U.S. Pat. No. 4,473,543, is such a device. It can operate in a temperature range which is suitable for processing gasoline and is also easily configured into a small compact unit which is suitable for vehicular use.
While gasoline is considered to be the fuel of choice, circumstances may warrant the use of other fuels such as natural gas, propane or methanol, for example. With these other fuels, the fuel processing system would continue to include an autothermal reformer because of size and weight benefits.
Therefore what is needed is a fuel cell power plant for vehicles that starts instantly and uses a fuel processing unit which is light weight, compact and capable of processing gasoline, or the like fuels which contain sulfur compounds. This would be highly desirable from an environmental viewpoint in the reduction of pollutants and a more efficient use of natural resources.